Quarter-Bridge Type I

The following figure shows how to position a strain gage resistor in an axial configuration for the quarter-bridge type I.

The following figure shows how to position a strain gage resistor in a bending configuration for the quarter-bridge type I.

Quarter-bridge type I strain gage configurations have the following characteristics:

• A single active strain gage element mounted in the principle direction of axial or bending strain.
• A passive quarter-bridge completion resistor, known as a dummy resistor, in addition to half-bridge completion.
• Temperature variation decreasing the accuracy of the measurements.
• Sensitivity at 1000 µε is ~ 0.5 mV_out / V_EX input.

Quarter-Bridge Type I Circuit Diagram

The following symbols apply to the circuit diagram:

• R₁ is the half-bridge completion resistor.
• R₂ is the half-bridge completion resistor.
• R₃ is the quarter-bridge completion resistor, known as a dummy resistor.
• R₄ is the active strain gage element measuring tensile strain (+ε).
• V_EX is the excitation voltage.
• R_L is the lead resistance.
• V_CH is the measured voltage.

The following equation converts voltage ratios to strain units for quarter-bridge configurations.

where V_r is the voltage ratio that virtual channels use in the voltage-to-strain conversion equation, GF is the gage factor, R_L is the lead resistance, and R_g is the nominal gage resistance.